This invention relates to a projection optical system and a projection exposure apparatus using the same, particularly suitable for manufacture of devices such as ICs, LSIs, magnetic heads, liquid crystal panels, or CCDs, for example, having a very fine structure. More specifically, the invention is suitably usable in a microdevice manufacturing apparatus of step-and-repeat type or step-and-scan type, called a stepper, for projecting and printing a pattern of a reticle on a photosensitive substrate with a high resolution.
Semiconductor manufacturing technologies for production of semiconductor devices, for example, have recently been advanced notably, and microprocessing technologies have also been improved significantly.
Particularly, in optical processing technologies, a reduction projection exposure apparatus, called a stepper, having a resolution of submicron order is used widely. For further improvements in resolution, enlargement of the numerical aperture (NA) of a projection optical system or narrowing the wavelength of exposure light has been attempted.
A projection optical system in a projection exposure apparatus for printing a pattern of a semiconductor device such as IC or LSI, for example, on a wafer of silicon, for example, should have a very high resolution.
Generally, the resolution of a projected image becomes higher with use of a shorter wavelength. Thus, it is desired to use a light source of shorter wavelength.
An example of such a short wavelength light source is an excimer laser. Excimer lasers use a laser medium of ArF or KrF, for example.
With regard to the wavelength region of such a short wavelength light source, only silica (quartz) and fluorite are usable as a glass material for lenses. This is mainly because of smallness of the transmission factor. Even when silica or fluorite is used, if an optical system has many lenses and a large total glass material thickness, there will occur inconveniences such as a shift of the focal point position due to heat absorption by the lens, for example.
Proposals for a reduction type projection optical system, reducing the number of constituent lenses of an optical system and the total lens glass material thickness, have been made (Japanese Published Patent Application, Publication No. 48089/1995, and Japanese Laid-Open Patent Application, Laid-Open No. 128592/1995). Further, a projection optical system being structured telecentric on both of the object side and the image side, has been proposed (Japanese Laid-Open Patent Applications, Laid-Open No. 34593/1993 and No. 197791/1998).
The projection optical systems as proposed in these documents use an aspherical surface lens having an aspherical surface formed on one lens face thereof, and the face (back side face) on the opposite side is formed by a spherical surface.
Generally, if the bottom or opposite face of an aspherical lens is to be formed into a spherical surface, making an aspherical surface itself requires very complicated works. Thus, it takes much time to make the lens. Further, there is a difficulty in optical axis registration between the aspherical surface and the spherical surface. As a result of it, the imaging performance of an assembled projection optical system may be degraded.
It is an object of the present invention to provide a projection optical system and/or a projection exposure apparatus having the same, in which the number of constituent lenses is reduced but a high resolving power and a wide exposure region are assured.
It is another object of the present invention to provide a projection optical system for use in a projection exposure apparatus, having an aspherical surface lens which can be produced with a relatively simple work and adjustment.
In accordance with an aspect of the present invention, there is provided a projection optical system for projecting a pattern of a mask onto a wafer, wherein said projection optical system includes at least one aspherical surface lens having an aspherical surface on one side and a flat surface on the other side.
In one preferred form of this aspect of the present invention, all aspherical surfaces of said projection optical system may satisfy a relation |xcex94ASPH/L| greater than 1xc3x9710xe2x88x926 where xcex94ASPH is the aspherical amount of the aspherical surface and L is an object-to-image distance of said projection optical system.
Here, the aspherical amount refers to a deviation between a spherical surface, following a design curvature radius, and an aspherical surface with respect to an optical axis direction.
Said projection optical system may include a plurality of lens groups including a positive refractive power lens group and a negative refractive power lens group, and a relation |Lxc3x97xcfx860| greater than 17 may be satisfied where L is an object-to-image distance and xcfx860 is the sum of powers of the negative lens group or groups.
The aspherical surface may be formed on a surface being in a range satisfying a relation, from the object side, |hb/h| greater than 0.35 where h is a height of an axial marginal light ray, and hb is a height of a most abaxial chief ray.
The aspherical surface may be formed on a surface satisfying a relation hea/hmax greater than 0.70 where hea is an effective diameter of the surface, and hmax is a largest effective diameter of said projection optical system.
The aspherical surface may be formed on a surface being in a range satisfying a relation, from the object side, |hbh| greater than 0.35 where h is a height of an axial marginal light ray, and hb is a height of a most abaxial chief ray.
The aspherical surface may be formed on a surface satisfying a relation hea/hmax greater than 0.70 where hea is an effective diameter of the surface, and hmax is a largest effective diameter of said projection optical system.
The projection optical system may satisfy a relation |xcex94ASPH/L| less than 0.02 where xcex94ASPH is the aspherical amount of the aspherical surface and L is an object-to-image distance of said projection optical system.
The projection optical system may satisfy a relation |Lxc3x97xcfx860| less than 70 where L is an object-to-image distance and xcfx860 is the sum of powers of a negative lens group.
The projection optical system may satisfy a relation |hb/h| less than 15 where h is a height of an axial marginal light ray, and hb is a height of a most abaxial chief ray.
In another preferred form of this aspect of the present invention, said projection optical system may have at least one aspherical surface, and wherein all lenses provided with an aspherical surface are so structured that an aspherical surface is formed on one side and a flat surface is formed on the other side.
In one preferred form of this aspect of the present invention, all aspherical surfaces of said projection optical system may satisfy a relation |xcex94ASPH/L| greater than 1xc3x9710xe2x88x926 where xcex94ASPH is the aspherical amount of the aspherical surface and L is an object-to-image distance of said projection optical system.
Said projection optical system may include a plurality of lens groups including a positive refractive power lens group and a negative refractive power lens group, and a relation |Lxc3x97xcfx860| greater than 17 may be satisfied where L is an object-to-image distance and xcfx860 is the sum of powers of the negative lens group or groups.
The aspherical surface may be formed on a surface being in a range satisfying a relation, from the object side, |hb/h| greater than 0.35 where h is a height of an axial marginal light ray, and hb is a height of a most abaxial chief ray.
The aspherical surface may be formed on a surface satisfying a relation hea/hmax greater than 0.70 where hea is an effective diameter of the surface, and hmax is a largest effective diameter of said projection optical system.
The aspherical surface may be formed on a surface being in a range satisfying a relation, from the object side, |hb/h| greater than 0.35 where H is a height of an axial marginal light ray, and hb is a height of a most abaxial chief ray.
The aspherical surface may be formed on a surface satisfying a relation hea/hmax greater than 0.70 where hea is an effective diameter of the surface, and hmax is a largest effective diameter of said projection optical system.
The projection optical system may satisfy a relation |xcex94ASPH/L| less than 0.02 where xcex94ASPH is the aspherical amount of the aspherical surface and L is an object-to-image distance of said projection optical system.
The projection optical system may satisfy a relation |Lxc3x97xcfx860| less than 70 where L is an object-to-image distance and xcfx860 is the sum of powers of a negative lens group.
The projection optical system may satisfy a relation |hb/h| less than 15 where h is a height of an axial marginal light ray, and hb is a height of a most abaxial chief ray.
In accordance with another aspect of the present invention, there is provided a projection exposure apparatus including a projection optical system as recited above, for projecting a pattern of a reticle onto a photosensitive substrate in accordance with one of a step-and-repeat process and a step-and-scan process.
In accordance with a further aspect of the present invention, there is provided a device manufacturing method for projecting a pattern of a reticle onto a wafer by use of a projection optical system as recited above, and for producing a device through a development process to the wafer.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.